During polymerizations with aromatic diacids, 2-methylpentamethylenediamine cyclizes to 3-methylpiperidine. 3-Methylpiperidine is incorporated into the polymer as an end capper which reduces the polymer molecular weight. Also the cyclization reaction leads to a significant loss of diamine (3-5%) during the polymerization. The addition of formic acid at the beginning of the polymerization significantly reduces cyclization of 2-methylpentamethylenediamine. With formic acid present a higher molecular weight polymer can be made with less yield loss to 3-methylpiperidine.
Polymers of 2-methylpentamethylenediamine and aromatic diacids, such as with hexamethylenediamine and terephthalic acid, have higher melting points, better high temperature properties and better dimensional stability than nylon 66. It is difficult to make these polymers with a satisfactory molecular weight because of the cyclization reaction and incorporation of 3-methylpiperidine as an end capper. A large excess (about 4%) of 2-methylpentamethylenediamine is required because of the extent of cyclization.